In a current wireless network system, to avoid or reduce interference between different wireless technologies, a fixed spectrum allocation policy is widely used. Spectrum allocation is performed by a relevant national institution or a standard organization, to separately allocate a part of spectrums to specified institutions to perform particular services. A spectrum that is specified to be allocated is referred to as a licensed spectrum, and a spectrum that is not specified to be allocated is referred to as an unlicensed spectrum. A communications device may communicate with a peer device by using the licensed spectrum and the unlicensed spectrum. Usually, the licensed spectrum is stable and sustainable, and the unlicensed spectrum is relatively unstable and unsustainable. Currently, most WiFi (Wireless Fidelity) devices work on unlicensed spectrums. Unlicensed spectrums in China now include frequency bands such as 2.4 to 2.4835 GHz and 5.725 to 5.850 GHz. According to a spectrum white paper latest released by the Federal Communications Commission (FCC for short), unlicensed spectrum resources may be more than licensed spectrum resources. Therefore, if a Long Term Evolution (LTE) device is applied to an unlicensed spectrum, an unlicensed spectrum resource may be effectively used, thereby increasing a data transmission amount, and meeting ever-growing mobile broadband service requirements.
However, unlike the licensed spectrum, the unlicensed spectrum cannot be used stably for a long time. A situation in which the unlicensed spectrum is available in a period of time, but is unavailable in a next period of time may occur. For this situation, the originally available unlicensed spectrum becomes unavailable, but a data retransmission process is not ended, and continues waiting for a proper occasion on the unlicensed spectrum. As a result, obviously data cannot be sent in time, and packet loss may occur because of a timeout, thereby affecting timeliness and even stability of data transmission.